1. Field of the Invention
The present invention generally relates to systems and methods to cool the nacelle and the heat generating components of an offshore wind turbine, with a provision to warm them before a cold start-up. More particularly, the present invention relates to a system to cool the air inside the nacelle and to cool the heat generating components such as the drivetrain, the electrical generator, the converter, and the transformer of an offshore wind turbine. The system can also be used to warm the air inside the nacelle and/or to warm one or more of these components before a cold turbine start-up.
2. Related Art
A wind turbine converts the kinetic energy of the wind into electrical energy through its rotor, drivetrain, electrical generator, and converter. An electrical transformer converts the low voltage output from the converter into a high voltage output before the output is sent to a substation at a wind farm. A wind turbine nacelle houses these mechanical and electrical components, namely, the drivetrain, the electrical generator, the converter, and the transformer (which is usually located in the nacelle to reduce power loss due to low voltage electrical transmission). The wind turbine nacelle also houses the components of the hydraulic system needed for blade pitching and nacelle yawing.
These components generate a significant amount of heat while the wind turbine is operating. For their protection and their efficient operation, the heat generated by such components has to be continuously removed. This is typically done by circulating a coolant through the heat exchangers built into these components. The coolant then transports the heat from these components and dissipates it to the ambient air with the help of air-cooled radiators mounted on the outside of the nacelle. The coolant can be any fluid that is typically used in low temperature heat exchangers, such as a mixture of ethylene glycol and water that does not freeze during cold weather. The heat generated by the drivetrain, and that by the hydraulic system, is dissipated to the coolant through liquid-to-liquid heat exchangers in the lubricating oil and the hydraulic fluid sumps, respectively.
In addition to dissipating the heat to the coolant, the wind turbine components also dissipate heat from their outer surfaces to the surrounding air. Components such as the transformer dissipate the heat primarily to the surrounding air. Thus, the air inside the nacelle needs to be either continuously replaced by fresh cooler air (an open airflow system) or cooled and re-circulated (a closed airflow system). In a turbine with an open airflow system, typically used in onshore turbines, the ambient air usually enters through one or more inlets at the nacelle bottom, and the warmer air exits to the outside through the outlets at the nacelle rear top. The outlet fans help the airflow through the nacelle and over the heat generating components. Thus, the ambient air is typically used as the heat sink to cool the heat generating components of a wind turbine.